Rapid thermal etch and rapid thermal oxidation

ABSTRACT

At least both a rapid thermal etch step and a rapid thermal oxidation step are performed on a semiconductor substrate in situ in a rapid thermal processor. A method including an oxidation step followed by an etch step may be used to remove contamination and damage from a substrate. A method including a first etch step followed by an oxidation step and a second etch step may likewise be used to remove contamination and damage, and a final oxidation step may optionally be included to grow an oxide film. A method including an etch step followed by an oxidation step may also be used to grow an oxide film. Repeated alternate in situ oxidation and etch steps may be used until a desired removal of contamination or silicon damage is accomplished.

RELATED APPLICATIONS

This is a continuation of U.S. patent application Ser. No. 09/189,920,filed Nov. 12, 1998, entitled “Rapid Thermal Etch and Rapid ThermalOxidation”, now U.S. Pat. No. 6,194,327, which is a continuation of U.S.patent application Ser. No. 08/582,587, filed Jan. 3, 1996, entitled “InSitu Rapid Thermal Etch and Rapid Thermal Oxidation”, now U.S. Pat. No.5,869,405, which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

The Field of the Invention

The present invention relates to the manufacture of semiconductordevices, and particularly to the removal of damage or contamination,especially oxide containing contamination, from a semiconductorsubstrate, and the growth of extremely high quality oxide films duringthe manufacture of a semiconductor device. More particularly, thepresent invention is directed to improved methods for removingcontamination and damage a substrate, and for growing contamination- anddefect-free oxide films on a substrate, by in situ rapid thermal etchand rapid thermal oxidation.

The Relevant Technology

Many of the steps performed in the manufacture of semiconductor devicesrequire that contamination or damage be removed from a siliconsubstrate. The various processes typically used to remove contaminationor damage generally may be classed as wet cleaning methods or drycleaning methods. Wet cleaning of various types can introduce many typesof contamination. Placing the substrate in contact with liquids tends toresult in particulate contamination of the substrate. Dry cleaningmethods employing plasma energy or similar energy sources cansubstantially avoid causing particulate contamination, but can causelattice damage to the substrate. Dry cleaning methods without plasma orsimilar energy sources to assist the cleaning processes can avoid damageto the substrate, but are typically too slow for cost-effectivemanufacturing.

Deposition of extremely high-quality oxide films is also generallyrequired in the manufacture of semiconductor devices, such as indeposition of gate oxides in state of the art field-effect transistors.Production of such extremely-high quality oxide films requires that thesubstrate be contamination-free and damage-free.

Effective, high-throughput cleaning methods resulting in acontamination-free and damage-free substrate are thus needed.

SUMMARY AND OBJECTS OF THE INVENTION

An object of the present invention is to provide improved methods forremoval of contamination and damage of a substrate.

Another object of the present invention is to provide methods forremoval of contamination and damage of a substrate, which methodsprovide increased throughput through the performance of multiple processsteps in situ.

Yet another object of the present invention is to provide methods forremoval of contamination and damage of a substrate, which methodsinclude growing an extremely high-quality oxide film in situ afterremoval of said contamination and damage.

Still another object of the present invention is to provide methods forremoval of contamination and silicon damage of a substrate due to stressfrom plasma etching or stress in the area of a field isolation regionsuch as a LOCOS region, which methods may be readily performed bycurrent processing equipment with little or no modification thereof

In accordance with the present invention, at least both a rapid thermaletch step and a rapid thermal oxidation step are performed on asemiconductor substrate in situ in a rapid thermal processor. Variouscombinations of etch steps and oxidation steps may be employed forvarious purposes. A method including an oxidation step followed by anetch step may be used to remove contamination and damage from asubstrate. A method including a first etch step, followed by anoxidation step and a second etch step, may likewise be used to removecontamination and damage, and a final oxidation step may optionally beincluded to grow an oxide film. A method including an etch step followedby an oxidation step may also be used to grow an oxide film. Theperformance of the various steps in situ in a rapid thermal processorimproves throughput and reduces the opportunity for contamination. Theelevated temperatures in the rapid thermal processor environmentincrease the reaction rates for the etch step without causing radiationdamage to the substrate. The extremely short ramp up times andprocessing times of the rapid thermal processor keep diffusion effectsquite small preventing unwanted migration of dopants and impurities.These methods result in an extremely clean, damage-free substrate.

These and other objects and features of the present invention willbecome more fully apparent from the following description and appendedclaims, or may be learned by the practice of the invention as set forthhereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the manner in which the above-recited and other advantagesand objects of the invention are obtained may be more fully explained, amore particular description of the invention briefly described abovewill be rendered by reference to specific embodiments and applicationsthereof which are illustrated in the appended drawings. Understandingthat these drawings depict only typical embodiments and applications ofthe invention and are not therefore to be considered to be limiting ofits scope, the invention will be described and explained with additionalspecificity and detail through the use of the accompanying drawings inwhich:

FIG. 1 is a flow chart of steps included in certain preferred methodsaccording to t present invention.

FIG. 2 is a partial cross section of a partially formed semiconductordevice with which the methods of the present invention may bebeneficially employed.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention provides particularly advantageous cleaning of asubstrate which avoids introduction of particulate contamination andsubstrate damage by performing at least both one rapid thermal etch andone rapid thermal oxidation in situ in the same rapid thermal processor.The methods of the present invention also optionally include in situgrowth of an extremely high-quality oxide film after cleaning isperformed. The order and number of rapid thermal etch steps and rapidthermal oxidation steps may be varied in particular preferredembodiments as will be described below.

FIG. 1 is a flow chart of steps in certain currently preferred methodsaccording to the present invention. The flow chart of FIG. 1 includesfive alternate paths: A1, A2, B1, B2, and B3. Each path includes atleast a rapid thermal etch step and a rapid thermal oxidation step. Eachpath provides a different combination of rapid thermal etch steps andrapid thermal oxidation steps according to various preferred methods ofthe present invention. Each of the steps shown in the flow chart of FIG.1 are to be performed in situ in a rapid thermal processor. In situperformance of the various steps ensures a minimum of contamination andincreases throughput.

The rapid thermal oxidation steps in the flow chart of FIG. 1 arepreferably performed by maintaining a substrate at a desired elevatedtemperature in a process chamber of a rapid thermal processor whileflowing oxygen through the process chamber of the rapid thermalprocessor and around the substrate. Other oxidizing gas flows may alsobe employed. The temperature of the substrate for the oxidation stepsshould generally be within a range of about 800 to 1200° C., and mostpreferably within a range of about 950 to 1050° C.

The rapid thermal etch steps in the flow chart of FIG. 1 are similarlypreferably performed by maintaining a substrate at a desired elevatedtemperature in a process chamber of a rapid thermal processor, whileflowing an etchant through the process chamber of the rapid thermalprocessor and around the substrate. The etchant is to be used in neithera wet etch process nor a plasma dry etch process. Rather, the etchantflowed into the rapid thermal processor can be non-plasma fluorine gas(F₂) and non-plasma hydrogen gas (H₂). The etchant used is preferablyhydrogen, fluorine, or a mixture of hydrogen and fluorine, supplied tothe process chamber in a mixture with an inert gas or nonreactive gas,although any etchant suitable for high temperature use may be employed.The flow rate of hydrogen and fluorine is preferably within a range of3% to 25% of the total gas flow rate.

The temperature at which the etch steps are performed may be identicalto or different from the temperature at which the oxidation steps areperformed, in which case an appropriate ramp up or ramp down of thetemperature is used between steps. The temperature for the etch stepsshould be within a range of about 800 to 1200° C., and preferably withina range of 900 to 1050° C. A ramp-down to near ambient temperatures mayoptionally be employed between steps if desired, allowingtemperature-driven control over the termination of the preceding step.

Additionally, a gas non-reactive in the particular process, such asnitrogen, or an inert gas non-reactive in virtually every process, suchas argon, may optionally be flowed through the process chamber betweensteps.

Path A1 of the flow chart of FIG. 1 illustrates a substrate cleaning anddamage removal method including a rapid thermal oxidation step followedby a rapid thermal etch step. The oxidation step oxidizes particle andfilm contaminants and damaged substrate areas, if any. The etch stepremoves the oxidized material, leaving behind a contamination-free,undamaged substrate.

Path A2 includes the steps of path A1 but adds at the end a secondoxidation step for growing a high quality oxide on the just-cleanedsubstrate. Path A2 may thus be employed where it is desired to clean asubstrate and then grow an oxide film thereon.

Path B2 of the flow chart of Figure is similar to path A1, except that arapid thermal etch step precedes the rapid thermal oxidation step. PathB2, like path A1, is useful to provide a contamination-free, undamagedsubstrate, particularly where a first oxide film is present before theprocessing shown in FIG. 1. The first etch step then removes the firstoxide film so that the oxidation step can more readily oxidizecontaminants and damaged areas to create a second oxide film which isthen removed by the second etch step.

Path B3 of the flow chart of FIG. 1 is similar path B2, except that asecond oxidation step is added after the second etch step. The firstetch step, the first oxidation step, and the second etch step of path B3function to clean a substrate as explained above with respect to pathB2. The second oxidation step then is used to grow a contamination- anddefect-free oxide film Path B3 may thus be employed where it is desiredto clean a substrate and then grow an oxide film thereon.

Path B1 provides an alternate method for cleaning a substrate andgrowing a film thereon. Where the substrate has fewer contaminants anddamage, or the removal of any contaminants and damage is less critical,path B1 may be used. In the method represented by path B1, an etch stepremoves any oxide from the substrate, along with any contamination ordamage associated therewith, and then an oxidation step grows an oxidefilm Path B1 may be alternatively used a first time and a second timewith additional process steps interposed between the first and secondtimes. The first time of processing according to path B1 then grows anoxide film during the oxidation step which is later removed during theetch step of the second time of processing according to path B1, afterwhich a final contamination- and defect-free oxide film is grown in theoxidation step.

The sequence of rapid thermal etch and rapid thermal oxidation steps maybe repeated as needed as shown by the dashed arrows in FIG. 1. Thusmethods having more steps than three or four, as shown in paths A2 andB3 for example, are available. Multiple alternating oxidation and etchsteps are particularly useful where the substrate being cleaned is verysensitive to stress. Each oxidation step can be permitted to grow only arelatively thin oxide film, in a range of about 25 to 40 Angstroms, forexample, thus avoiding the stresses created during the growth of thickeroxides.

The above inventive methods may be employed at any suitable stage ofsemiconductor fabrication. The methods which include growth and removalof an oxide film are particularly suited for producing a highly cleanand defect-free substrate. The growth of the oxide film extends downwardinto the substrate, such that even subsurface contamination is removedwhen the oxide film is removed.

The above methods may be employed, for example, during the formation ofactive areas and oxide gates in the fabrication of FET devices. Anexample process flow for formation of active areas and gate oxide mayinclude the steps shown in the first column of Table I below.

The method of path B1 of FIG. 1 may be used either to replace thetypical means of removing the pad oxide and growing the sacrificialoxide in steps 6 and 7 of the example process flow of Table I, or toreplace the typical means of removing the sacrificial oxide and growingthe gate oxide in steps 12 and 13 of the example process flow of TableI, or both, as shown in the second column of Table I. The method of pathB1 allows the combination of two typically separate steps into one shortprocess, allowing for a potentially significant increase in throughput.

The method of path B3 of FIG. 1 may also be employed in a modifiedprocess flow for formation of active areas and gate oxide. As shown inthe third column of Table I, the pad oxide removal step and sacrificialoxide growth step, steps 6 and 7 of the example process flow of Table I,may be omitted. The subsequent implants are then performed through thepad oxide layer. In place of steps 12 and 13 of the example process flowof Table I, the method of path B3 is then employed to remove the padoxide, grow a sacrificial oxide, remove the sacrificial oxide, and growthe gate oxide.

In the examples in Table I, the etch step of the first application ofpath B1 or the first etch step of path B3 must be of sufficient durationto remove the pad oxide. The preferred pad oxide thickness is in a rangeof about 100 to 250 Angstroms. The sacrificial oxide grown in theoxidation step of the first application of path B1 or in the firstoxidation step of path B3 is preferably in a range of about 250-350Angstroms thick, and most preferably about 300 Angstroms thick. The gateoxide grown in the oxidation step of the second application of path B1,or in the second oxidation step of path B3, is preferably in a range ofabout 80 to 120 Angstroms thick, and most preferably about 100 Angstromsthick.

TABLE I Step EXAMPLE PROCESS FLOW PROCESS FLOW No. PROCESS EMPLOYINGEMPLOYING FLOW PATH B1 PATH B3 1 Pad Oxide Pad Oxide Pad Oxide 2 NitrideDeposition Nitride Deposition Nitride Deposition 3 Active Area ActiveArea Active Area Patterning Patterning Patterning 4 Field OxidationField Oxidation Field Oxidation 5 Remove Nitride Remove Nitride RemoveNitride 6 Remove Pad Oxide PATH B1 7 Grow SAC Oxide 8 Implant ImplantImplant 9 LIF Pattern LIF Pattern LIF Pattern 10 Implants ImplantsImplants 11 Remove Resist Remove Resist Remove Resist 12 Remove SACOxide PATH B1 PATH B3 13 Grow Gate Oxide

As a further example, the inventive methods diagrammed in FIG. 1 mayalso be employed during preparation of the source/drain regions of asubstrate for buried contact deposition. Prior art processes use a wetetch process or a plasma dry etch process to remove a native oxide layerin the buried contact region. The method of path B2 of FIG. 1 may bebeneficially used to remove the native oxide layer and any othercontaminants or damage without introducing additional damage orcontamination. Additional etch and oxidation steps may be included asindicated by the dashed line in FIG. 1.

A first etch step is preferably performed in hydrogen at a temperaturein a range of about 900-1200° C., most preferably 1000° C., for 5-15seconds, and most preferably 10 seconds. This is followed by anoxidation step performed in oxygen at a temperature in a range of about900-1200° C., most preferably 1000° C., for 20-40 seconds, and mostpreferably 30 seconds, to clean the surface by oxidizing it to produce asecond oxide layer with a thickness in a range of about 25 to 50Angstroms. This is followed by a second etch step performed in hydrogenat a temperature in a range of about 900-1200° C., most preferably 1000°C., for 20-40 seconds, and most preferably 30 seconds, to remove thesecond oxide layer. Additional identical oxidation and etch steps may beemployed as needed to remove all contamination and silicon damage. It ispresently preferred to perform at least four such identical oxidationand etch steps.

The above method is particularly useful to remove the so-called whiteribbon or Kooi effect. The white ribbon or Kooi effect is an area ofnitridized silicon damage that extends around the edges of an activearea. An example of the location of white ribbon is illustrated in FIG.2.

In FIG. 2, source/drain region 16 is formed in substrate 10. Substrate10 has formed thereon a gate stack 12. Source/drain region 16 is at theedge of an active area, i.e., next to a field oxidation region 14. Atthe edges of the active area next to field oxidation 14 is formed whiteribbon 18 which must be removed to permit the formation of a morereliable gate at the field edge. The above described alternatingoxidation and etch steps, all performed in situ in the same rapidthermal processor, may be utilized to remove white ribbon 18 withoutcausing damage to substrate 10 at source/drain region 16.

The method of path B2 may also be applied, in a manner similar to thatdescribed above, to formation of final contacts. With appropriatemodifications of temperature and etch chemistry to protect any metal(s)used, the method above may also be applied for the removal of oxidationand contamination prior to formation of vias. The method of path A1 ofFIG. 1 may alternatively be used in place of the method of path B2 whereremoval of a pre-existing oxide layer is not required.

The methods of the present invention may be performed in any standardrapid thermal processor provided with appropriate gas sources and flowcontrollers.

The present invention may be embodied in other specific forms withoutdeparting from its spirit or essential characteristics. The describedembodiments are to be considered in all respects only as illustrativeand not restrictive. The scope of the invention is, therefore, indicatedby the appended claims rather than by the foregoing description. Allchanges which come within the meaning and range of equivalency of theclaims are to be embraced within their scope.

What is claimed and desired to be secured by United States LettersPatent is:
 1. A method of processing a substrate during the fabricationof a semiconductor device, said method comprising: heating a substratehaving a first oxide layer thereon; etching in a rapid thermal processsaid first oxide layer to remove said first oxide layer, wherein etchingsaid oxide layer comprises exposing said first oxide layer to non-plasmafluorine gas (F₂) and non-plasma hydrogen gas (H₂); and oxidizing in arapid thermal process said substrate to form a second oxide layer. 2.The method as recited in claim 1, wherein oxidizing said substratecomprises exposing said substrate to oxygen gas.
 3. The method asrecited in claim 1, wherein etching said first oxide layer comprisesexposing said first oxide layer to a flow of fluorine gas and hydrogengas and a non-reactive gas, the flow rate of said fluorine gas and saidhydrogen gas together as a percentage of the total gas flow rate beingin a range of about 3% to 25%.
 4. The method as recited in claim 1,wherein said first oxide layer has a thickness in a range from about 100Angstroms to about 150 Angstroms, and said second oxide layer has athickness in a range from about 250 Angstroms to about 350 Angstroms. 5.The method as recited in claim 1, wherein said first oxide layer has athickness in a range from about 250 Angstroms to about 350 Angstroms andsaid second oxide layer has a thickness in a range from about 80Angstroms to about 120 Angstroms.
 6. The method as recited in claim 1,further comprising, after oxidizing said substrate: etching said secondoxide layer to remove said second oxide layer.
 7. The method as recitedin claim 6, wherein: etching said first oxide layer comprises etchingsaid substrate in an etchant gas at a temperature in a range from about800° C. to about 1200° C. for a time in a range from about 5 seconds toabout 15 seconds; oxidizing said substrate comprises oxidizing saidsubstrate in oxygen gas at a temperature in a range from about 800° C.to about 1200° C. for a time in a range from about 20 seconds to about40 seconds; and etching said second oxide layer comprises etching saidsecond oxide layer in an etchant gas at a temperature in a range fromabout 800° C. to about 1200° C. for a time in a range from about 20seconds to about 40 seconds.
 8. The method as recited in claim 6,wherein: etching said first oxide layer comprises etching said substratein an etchant gas at a temperature in a range from about 900° C. toabout 1050° C. for a time in a range from about 5 seconds to about 15seconds; oxidizing said substrate comprises oxidizing said substrate inoxygen gas at a temperature in a range from about 900° C. to about 1050°C. for a time in a range from about 20 seconds to about 40 seconds; andetching said second oxide layer comprises etching said second oxidelayer in an etchant gas at a temperature in a range from about 900° C.to about 1050° C. for a time in a range from about 20 seconds to about40 seconds.
 9. The method as recited in claim 6, further comprisingrepeating oxidizing said substrate and etching said second oxide layeruntil any previously present contamination and substrate damage isremoved, and wherein oxidizing said substrate comprises forming an oxidelayer having a thickness in a range from about 25 Angstroms to about 50Angstroms.
 10. The method as recited in claim 9, wherein repeatingetching said first oxide layer and oxidizing said substrate comprisesperforming etching said first oxide layer and oxidizing said substrateat least four times.
 11. The method as recited in claim 6, wherein:heating a substrate comprises heating a substrate having a white ribbonon the surface thereof; oxidizing said substrate comprises forming saidsecond oxide layer having a thickness in a range from about 25 Angstromsto about 50 Angstroms; and said method further comprises repeatingoxidizing said substrate and etching said second oxide layer until thewhite ribbon is removed from the substrate.
 12. The method as recited inclaim 11, wherein repeating etching said first oxide layer and oxidizingsaid substrate comprises performing etching said first oxide layer andoxidizing said substrate at least four times.
 13. The method as recitedin claim 6, further comprising repeating etching said first oxide layerand oxidizing said substrate so that etching said first oxide layer andoxidizing said substrate are performed a total of a least four times.14. The method as recited in claim 6, further comprising oxidizing saidsubstrate to form a third oxide layer.
 15. The method as recited inclaim 14, wherein said first oxide layer has a thickness in a range fromabout 100 Angstroms to about 250 Angstroms, said second oxide layer hasa thickness in a range from about 250 Angstroms to about 350 Angstroms,and said third oxide has a thickness in a range from about 80 Angstromsto about 120 Angstroms.
 16. A method of processing a substrate duringthe fabrication of a semiconductor device, said method comprising:oxidizing in a rapid thermal process substrate contaminants to transformat least a portion of said contaminants into oxidized material; andetching in a rapid thermal process said oxidized material to produce aclean substrate.
 17. The method as recited in claim 16, furthercomprising oxidizing said clean substrate so that an oxide is formed onsaid clean substrate.
 18. The method as recited in claim 16, whereinsaid oxidizing in a rapid thermal process is performed by exposing saidsubstrate contaminants to oxygen gas.
 19. The method as recited in claim16, wherein said etching is performed by exposing said oxidized materialto a non-plasma high-temperature etchant.
 20. The method as recited inclaim 16, wherein said etching is performed by exposing said oxidizedmaterial to non-plasma hydrogen gas (H₂).
 21. The method as recited inclaim 16, wherein said etching is performed by exposing said oxidizedmaterial to non-plasma fluorine gas (F₂).
 22. The method as recited inclaim 16, wherein said etching is performed by exposing said oxidizedmaterial to non-plasma fluorine gas (F₂) and non-plasma hydrogen gas(H₂).
 23. A method of processing a substrate during the fabrication of asemiconductor device, said method comprising: oxidizing substratecontaminants to transform at least a portion of said contaminants intooxidized material; etching in a rapid thermal process said oxidizedmaterial to produce a clean substrate; and oxidizing said cleansubstrate so that an oxide is formed on said clean substrate, wherein atleast one of said oxidizing substrate contaminants and said oxidizingsaid clean substrate is performed in a rapid thermal process.
 24. Themethod as recited in claim 23, wherein said etching is performed byexposing said oxidized material to non-plasma fluorine gas (F₂) andnon-plasma hydrogen gas (H₂).
 25. A method of processing a substrateduring the fabrication of a semiconductor device, said methodcomprising: etching substrate contaminants to produce a clean substrate;oxidizing in a rapid thermal process said clean substrate to form asecond oxide layer; and etching said second oxide layer, wherein atleast one of said etching substrate contaminants and said etching saidsecond oxide layer is performed in a rapid thermal process.
 26. Themethod as recited in claim 25, wherein at least one of said etchingsubstrate contaminants and said etching said second oxide layer isperformed with non-plasma fluorine gas (F₂) and non-plasma hydrogen gas(H₂).
 27. A method of processing a substrate during the fabrication of asemiconductor device, said method comprising: heating a substrate havinga first oxide layer thereon; rapid thermal etching said first oxidelayer to remove said first oxide layer, wherein etching said oxide layercomprises exposing said oxide layer to fluorine gas (F₂) and hydrogengas (H₂); and rapid thermal oxidizing said substrate to form a secondoxide layer.